Waveguide filters are often employed, for example, in microwave communication systems for the purpose of determining a system's frequency response characteristics. Such filters may operate in a single mode or may be of a dual mode type in which two electromagnetic propagated waves extend orthogonal to each other within the waveguide filter.
A typical waveguide filter comprises a symmetrical hollow body which may be cylindrical, for example, in the case of a circular waveguide, and is divided into a plurality of resonant cavities by partitions sometimes referred to as "septums" . In the case of a dual mode-type waveguide filter, each cavity defines two sections of the filter, thus, a dual mode waveguide filter having three cavities possesses six sections, including an input section and an output section. The mutually orthogonal electromagnetic fields are passed between adjacent cavities through intersecting slots defining a cross-shaped iris in each of the septums.
It is known to provide adjustable metallic screws which extend through the body of the filter into the cavities in order to effect electromagnetic coupling between orthogonal fields which are present in the same cavity. It is also known to effect coupling between mutually orthogonal fields which are respectively present in different cavities. The degree of coupling between the fields alters the device's frequency response by altering the stopband poles which determine such response.
The previous technique for coupling mutually orthogonal electromagnetic fields in different cavities involves the use of a coax cable external to the waveguide filter body which connects different sections of two cavities. This approach presents a number of problems, however. For example, the cables often result in spurious responses and are relatively complex in terms of the number of parts required to accomplish the task and the time required to assemble them. Moreover, the length of the cable is critical to frequency response and a considerable amount of time is necessary to determine the proper cable length so as to tune the filter properly.
The present invention is intended to overcome each of the deficiencies mentioned above.